Solid-state imaging device and solid-state imaging device manufacturing method

ABSTRACT

A solid-state imaging device  1  includes: a semiconductor substrate  11  on which pixels are placed like a matrix; and each of the pixels having a photoelectric conversion element  13  and a color filter layer  21  which is formed on the photoelectric conversion element  13 . The solid-state imaging device  1  includes resin parts  20  which are formed at the boundaries of these photoelectric conversion devices  13  which are adjacent to each other, each of the resin parts  20  having an upward convex shape. Each color filter layer  21  of the device is formed so that the color filter layer covers the area ranging from the summit of a resin part to the summit of an adjacent resin part, and each color filter layer  21  is thinner in the peripheral part than in the center part around the summit.

This application is a divisional of U.S. Application Ser. No.12/698,345, filed Feb. 2, 2010now U.S. Pat. No. 7,989,752, which is adivisional of U.S. Application Ser. No. 11/243,979, filed Oct. 6, 2005,now U.S. Pat. No. 7,683,302.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to a solid-state imaging device havingon-chip color filter layers and a manufacturing method of thesolid-state imaging device.

(2) Description of the Related Art

With the advancement of a color image forming technique, recent yearshave seen a remarkable growth in the use of a single-board color typesolid-state imaging device, the use being for a digital still cameramainly including CCD (Charge Coupled Device) type, and a mobile phonewith a camera mainly including CMOS type. This leads to the increase inthe demands for downsizing such a solid-state imaging device havingon-chip color filters and the day-by-day increase in the number ofpixels. However, in order to meet such demands for the solid-stateimaging device like this, the light-receiving area of a photoelectricconversion element 13, which is a light-receiving sensor, must bedownsized. This is becoming a cause for deteriorating photoelectricconversion characteristics (light sensitivity) which are a primalcharacteristic of a solid-state imaging device.

For example, main optical sizes of solid-state imaging devices to bemounted on digital still camera ranges from a third inch to a fourthinch, and further downsizing to a sixth inch or to below a sixth inch isbeing considered. Also, the number of pixels is becoming greater up tothe range from 2M pixels to 5M pixels, and it is considered to increasethe number exceeding 5M pixels. Therefore, there emerges a need toestablish a technique for maintaining the primal characteristics of asolid-state imaging device such as light sensitivity, color mixturebetween adjacent pixels and nonuniform tone of lines even in the case ofdownsizing a light-receiving area and increasing the number of pixels.

Here will be provided detailed description of this. Increasing thenumber of pixels without downsizing the pixel size causes the increasein the chip size, resulting in making the size of a solid-state imagingdevice larger. This means that the downsizing of the pixel size must beperformed in parallel. In general, downsizing the pixel size leads todownsizing a photoelectric conversion element 13 represented by aphotodiode, resulting in the deterioration in light sensitivity. Inorder to improve light sensitivity, a number of countermeasures havebeen taken. Especially, there have been proposed a number of structures,manufacturing methods and the like concerning a microlens which isformed on such a pixel.

Also, downsizing the pixel size becomes a cause for deteriorating notonly light sensitivity but also various color characteristics stemmingfrom a color filter layer. In general, making the pixel size finercauses deterioration in the dimensional accuracy of a color filter,resulting in the deterioration in characteristics such as color mixturebetween pixel filters which are adjacent to each other, nonuniform toneof lines, and sensitivity variations between pixel filters.

Therefore, the importance of on-chip color filter layers in asolid-state imaging device is increasingly becoming greater, and thusthere is a demand for establishing a technique with which thedeterioration of the characteristics such as color mixture, nonuniformtone of lines and sensitivity variations can be prevented.

FIG. 1 to FIG. 3 each depicts a sectional view of a pixel of aconventional solid-state imaging device.

These solid-state imaging devices 30 and 40 are each formed in thefollowing way: forming a P-type semiconductor well region 12, whichbecomes second electric conductive type, on a semiconductor substrate 11which is made of a first electric conductive type (for example, N type)silicon semiconductor; and then forming an N-type semiconductor regionon the P-type semiconductor well region 12, a N-type semiconductorregion and a P-type semiconductor well region 12 constitute aphotoelectric conversion element 13. The respective photoelectricconversion elements 13 are formed in array shapes and arranged in amatrix form.

Further, on the boundaries of photoelectric conversion elements 13, forexample, a conversion electrode 15 which is made of polycrystallinesilicon is formed through the gate insulation film 14. On the conversionelectrode 15 an inter-layer insulation film 16 which covers thisconversion electrode 15 is formed. Also, on the rest of the wholesurface, in other words, on the inter-layer insulation film 16 excludingthe apertures of the photoelectric conversion elements 13, for example,a light-shielding film 17 which is made of AL, W and the like is formed.After that, the light-shielding film 17 and the gate insulation film 14are covered with a surface protection film 18.

Further, a first transparent planarization film 19 is filled with eachconcave part above a photoelectric conversion element 13. After that, inthe case of a solid-state imaging device 30, color filter layers 31G,31B and 31R are respectively formed on each photoelectric conversionelement 13. In contrast, in the case of a solid-state imaging device 40,color filter layers 41G, 41B and 41R are respectively formed on eachphotoelectric conversion element 13. In both the cases, a secondtransparent planarization film 42 is formed on the color filter layers31G, 31B and 31R, and also the color filter layers 41G, 41B and 41R, andon-chip microlenses 43 are formed on the second transparentplanarization film 42, the on-chip microlenses 43 collecting incidentlight to the respectively corresponding photoelectric conversionelements 13.

The first transparent planarization film 19 is for forming stable colorfilter layers 31 and 41 and for making the ground flat. The secondtransparent planarization film 32 is for planarizing the color filterlayers 31 and 41 as the ground layer so as to form on-chip microlenses43 accurately.

Such color filter layers 31 and 41 are made of one of the following twotypes of color filter layers: primary color filter layers which are madeof red, green and blue filters; and complementary color filter layerswhich are made of yellow, cyan and magenta filters.

Also, the material used for the color filter layers 31 is pigmentdispersion type and has excellent light-resistance and heat resistance.A representative of such a material is a mixture of: pigments; adispersion agent; a photosensitive material; a resin; and the like.Color filter layers 31 are formed, according to a color resist methodfor obtaining a desired type of color filters, by performing a selectiveexposure process and a development process of a photo-resist filmcontaining such a material. In this way, the solid-state imaging device30 can provide the following two countermeasures for realizinghigh-definition against downsizing of pixels: slimming down a pigmentfilter which realizes improvement in the dimensional accuracy of colorfilter layers, and preventing nonuniform tone of lines, sensitivityvariations and color mixture between color filter layers which areadjacent to each other; and making pigment particles finer. By means ofthe above-listed countermeasures, a color S/N ratio is being improved.

Also, the material which is used for the color filter layers 41 is madeof a pigmented dye instead of a pigment and the like. The color filterlayers 41 are formed, according to a color resist method for formingdesired color filters, by performing a selective exposure process and adevelopment process of a photo-resist film containing a mixture of suchmaterials. Recent years have seen an accelerated research anddevelopment on this material, as a dye-containing color-resist whichdoes not contain a fine particle, which can replace a pigment-dispersioncolor-resist. Some of such color-resists become commercially practical,in other words, some of them have been used for color filter layers ofsolid-state imaging devices (Refer to Reference Document 1: JapaneseLaid-Open Patent Application No. 11-337715.).

The improvement example disclosed in the Patent Document 1 is forconcurrently simplifying a manufacturing process and improvinglight-resistance and heat-resistance by means of making dyes intopigmented dyes in order to obtain desired spectral characteristics.

However, slimming down the pigment-dispersion filter used for aconventional solid-state imaging device 30 requires that a certaindegree of film thickness be secured in order to obtain desired spectralcharacteristics, resulting in placing a restriction in slimming down.Further, making pigment particles finer involves a great difficulty, andit is impossible to prevent the diameter of secondary particles fromincreasing through re-aggregation even if those particles are once madefiner. Further, since pigment particles are present as long as thepigment dispersion color filter layers 31 are employed, the problemswhich are caused depending on the dimensional accuracy of the colorfilter layers 31 have not yet been fundamentally solved, the problemsbeing related to the color characteristics such as nonuniform tone oflines, color mixture, sensitivity variations and color S/N ratios.

This will be described below more specifically. The dimensional accuracyis improved because the following countermeasures concerning the pigmentdispersion color filter layers 31 are taken: slimming down of a materialwhich is used for a color filter (an increase in the pigment content);an improvement in resolution by means of such a material; and acountermeasure in the manufacturing process. However, there is a need toconsider the influence of the particle size of a pigment which is usedas a primal material of the color filter layers 31 in order to decreasethe pixel size. Especially, since a pigment itself is considered to be aparticle in dimensional accuracy and the secondary particle diameter isapproximately 100 nm in general, great technical advancement is requiredto decrease the sizes of such particles down to 50 nm by taking acountermeasure of making such particles much finer. Also, whether or notdesired spectrum characteristics can be obtained in the case of makingparticles finer has not yet been sufficiently confirmed. Further, sincepigments are particles, it is inevitable that the taken image looksuneven and the color S/N ratios (signal to noise ratio) deteriorate evenin the case where such a countermeasure of making pigment particlesfiner is taken. Therefore, assumingly, an existing technique places alimit to the use of such a pigment dispersion color resist which has afiner particle for color filter layers 31 in a solid-state imagingdevice.

In other words, it is difficult for us to cause a conventionalsolid-state imaging device 30 to prevent the deterioration in lightsensitivity or color mixture between adjacent pixels only by slimmingdown such color filter layers accompanied by the reduction in the pixelsize. The cause of color mixture will be described below morespecifically. Color mixture occurs depending on the sectional edgeshapes of color filter layers. The edges of the color filters cannot becut vertically when they are formed. For this reason, a firstly-formedcolor filter layer has a trapezoid shape (the top surface dimension issmaller than the bottom surface dimension). Since a secondly-formed andthirdly-formed color filter layers are inserted into the gaps of thefirstly-formed color filter pattern, they also have a trapezoid shape,in other words, the top surface dimensions are smaller than the bottomsurface dimensions). Consequently, an oblique incident light passesthrough the edge parts of the color filter layers of adjacent pixels asshown in FIG. 1. This makes it impossible to obtain desired spectralcharacteristics, resulting in causing color mixture.

Also, there is a problem which makes pigment particles finer decreasesthe alignment margin because of a conventional sectional shape. This isbecause, in the case where a gap in arrangement is generated, obliqueincident light which passes through the edges of the color filter layersof adjacent pixels as shown in FIG. 1 causes color mixture, which makesit impossible to obtain desired spectral characteristics. Further, colormixture degree varies depending on the angle of oblique incident light,and there are other problems such as nonuniform tone of lines, flicker,color shading and sensitivity variations.

In the case of using the pigment type color filter layers 31, exposurelight randomly reflects on the surface of pigment particles and thus thelight reaches comparatively deeper part of the filter. In contrast, inthe case of the solid-state imaging device 40 for which thedye-containing color filter layers 41 are employed in order to improvethe color S/N ratios, light polymerization reaction advances only in theproximity of the surfaces, in other words, the non-reaction parts aredominant inside the filters because there is no random reflection on thesurfaces of the dye-containing type color filter layers 41.

A thermal process which is generally referred to as Post Exposure Bake(PEB) is performed after exposure in order to accelerate such reactioninside the filters. At this time, performing this process under anappropriate temperature is very important. This is because it isimpossible to complete development in the case where the process isperformed under a too high temperature, and because cavities aregenerated on the sectional surfaces after development in the case wherethe process is performed under a too low temperature (Refer to FIG. 2).Therefore it is general that PEB conditions (temperature and time) aredetermined considering these problems. However, conventional techniqueis not sufficient to solve these problems even though it can slightlyimprove the problem of cavities which are generated on the sectionalsurfaces.

An example of such cavities is shown as cavity β in FIG. 3. The cavity βis generated at the boundary of the first layer and the second layerwhen the material to become the second layer is coated. Consequently,light is diffused making the problems worse, these problems being colormixture, nonuniform tone of lines and sensitivity variations. Further,the consequent thermal process causes the gas in the cavity β to expand,which causes the deformation of the color filter layer 41, thetransparent planarization film 42, and the microlens 43. This results inaffecting the reliability of the device.

SUMMARY OF THE INVENTION

The present invention is conceived considering the above-describedproblems. A primary object of the present invention is to provide (a) asolid-state imaging device which can improve the problems such as colormixture, nonuniform tone of lines and sensitivity variations betweencolor filter layers which are adjacent to each other and (b) amanufacturing method of the solid-state imaging device.

Also, a secondary object of the present invention is to provide (a) asolid-state imaging device which can further improve color S/N ratiosresulting in improving its reliability and (b) a manufacturing method ofthe solid-state imaging device.

In order to achieve the primary object, in the solid-state imagingdevice concerning the present invention, in which pixels are arrayedlike a matrix above a semiconductor substrate and each pixel has aphotoelectric conversion element 13 and a color filter layer formedabove the photoelectric conversion element 13, includes: resin partsformed above boundary parts between photoelectric conversion elements 13which are adjacent to each other so that each resin part constitutes anupward convex part formed above each boundary part, and in the device,each color filter layer is formed so that the color filter layer coversthe area ranging from the summit of a resin part to the summit of anadjacent resin part; and each color filter layer is formed so that thecolor filter layer is thinner in the peripheral part than in the centerpart around the summit.

This makes the edge shapes of the color filter layers vertical, and thusthe color filter layers can be formed accurately. Consequently, thedimensional accuracy of these color filters is improved, and it becomespossible to prevent oblique incident light from causing color mixture inadjacent color filter layers and improve the following problems whichare generated depending on dimensional accuracy: color mixture;nonuniform tone of lines; and sensitivity variations.

Also, compared to a conventional structure, the spectral dispersionbecomes weaker in the peripheral parts of the color filter layers thanin the center parts. Therefore, transparent light from the peripheralparts increases. Consequently, it is expected that the sensitivity of asolid-state imaging device is improved.

Note that color structure of a resin part may be a transparent film or acolored film (including black). Also, it is desirable that the width ofthe resin part be the same as or shallower than that of the boundaryregion. Also, it is desirable that the height of the resin part be lowerthan the surface of the center part of the color filter layer.

Also, in a second aspect of the present invention, in order to achievethe second object, in the solid-state imaging device concerning thepresent invention, each color filter layer is made of a dye-containingtype color resist.

In this way, the resin part slims down the peripheral parts of the colorfilter layers even in the case where such color filter layers are madeof dye-containing color resists. This advances the light polymerizationreaction in such a manner that it covers the whole peripheral parts ofthe films, and thus cavities at the edges are improved. This canconsequently prevent generation of cavities which is conventionallyobserved, and improves the problems of color mixture, nonuniform tone oflines and sensitivity variations, resulting in improving the reliabilityof the device. In addition, this makes it possible to make the surfacesof color filter layers become even although they are uneven in the casewhere dye-containing type color filters are used, and thus it becomespossible to improve the color S/N ratios.

Also, in the first aspect of the present invention, in the solid-stateimaging device concerning the present invention, the resin parts may beformed like a lattice above the boundary parts between photoelectricconversion elements 13 which are adjacent to each other, and each colorfilter layer may function as a concave lens.

Since the resin part is formed in a form of matrix at the boundarybetween itself and the adjacent photoelectric conversion element 13,each color filter layer has a sectional shape which is more upsurgedthan the photoelectric conversion area. Also, it becomes a concave lensin the case of a high-definition pixel size. Consequently, it has aneffect of effectively condensing incident light into the peripheral partof the surface to the photoelectric conversion elements 13 and improvingits sensitivity. Further, it is expected that it has an effect ofimproving color shading caused by oblique light.

Also, in the first aspect of the present invention, in the solid-stateimaging device concerning the present invention, each resin part may bemade of a material having a refractive index which is lower than arefractive index of each color filter.

This provides an effect of reducing incident light coming from anadjacent pixel when oblique incident light reaches the peripheral part.

Also, in the first aspect of the present invention, the solid-stateimaging device concerning the present invention may further includefirst transparent planarization films which are formed between each ofthe photoelectric conversion elements 13 and each of the color filterlayers so that the surfaces of the first transparent planarization filmsbecome flush with the surfaces of the boundary parts, and in the device,each color filter layer may be made of a material having a refractiveindex which is higher than a refractive index of each first transparentplanarization film.

This also provides an effect of reducing incident light coming from anadjacent pixel when oblique incident light reaches the peripheral part.

Also, in the fourth aspect of the present invention, the solid-stateimaging device concerning the present invention may further includesecond transparent planarization films which are formed on the colorfilter layers, and in the device, each second transparent planarizationfilm may be made of a material having a refractive index which is lowerthan the refractive index of each color filter layer.

This also provides an effect of reducing incident light coming from anadjacent pixel when oblique incident light reaches the peripheral part.

Also, in the sixth aspect of the present invention, the solid-stateimaging device concerning the present invention may further includemicrolenses which are formed on said second transparent planarizationfilms, and in the device, each microlens may be made of a materialhaving a refractive index which is higher than the refractive index ofeach second transparent planarization film.

In this way, these color filter layers serve as a lens. Therefore,placing microlenses on those color filter layers can improve the lightcondensing efficiencies of the color filter layers, and thus it becomespossible to improve the sensitivity of the color filter layers.

Also, in the seventh aspect of the present invention, in the solid-stateimaging device concerning the present invention, each microlens may bemade of a material having a refractive index which is higher than therefractive index of each color filter layer.

With this structure, the double lens effect, which is provided by thecombination of the color filter layer 21 which serves as a concave lensand the microlens 23 which serves as a convex lens, makes it possible tocondense light gradually and efficiently. Thus it is expected that itssensitivity is improved.

Also, the manufacturing method of the solid-state imaging deviceconcerning the present invention, in which pixels may be arrayed like amatrix above a semiconductor substrate and each pixel has aphotoelectric conversion element 13 and a color filter layer formedabove the photoelectric conversion element 13, includes: forming resinparts above boundary parts between photoelectric conversion elements 13which are adjacent to each other so that each resin part constitutes anupward convex part formed above each boundary part; and forming eachcolor filter layer which covers the area ranging from the summit of aresin part to the summit of an adjacent resin part so that the colorfilter layer is thinner in the peripheral part than in the center partaround the summit.

Also, in the ninth aspect of the present invention, the manufacturingmethod of the solid-state imaging device concerning the presentinvention may further include: forming microlenses on the color filterlayers, and in the forming of the resin parts in the method, the resinparts may be made of a mask for forming the microlenses.

Also, in the tenth aspect of the present invention, in the manufacturingmethod of the solid-state imaging device concerning the presentinvention, the resin parts may be made of a negative type resist, incontrast, the microlenses may be made of a positive type resist.

In this way, it becomes possible to form a resin part and a microlensonly using a mask, and thus it is possible to lower the cost formanufacturing a solid-state imaging device.

As described up to this point, the solid-state imaging device concerningthe present invention makes it possible to form respective filter layersaccurately. This is because, by means of forming a resin part having anupwardly convex sectional shape crossing a boundary between adjacentcolor filter layers of the respective pixels, the boundary regions ofthe color filter layers formed in sequence are slimmed down.Consequently, adjacent color filter layers are not affected by eachother when oblique incident light reaches them, and thus it becomespossible to improve the problems such as color mixture, nonuniform toneof lines, sensitivity variations and color shading.

Also, since the thickness of a combination part of the resin part andeach color filter layer placed on the resin part becomes thicker, itbecomes consequently possible to realize color filter layers which serveas a convex lens.

Also, since the sectional shape (edge shape) of each color filter layeris improved, the problem of cavities which are conventionally generatedaround the boundaries of the respective color filter layers is solved.In this way, it becomes possible to realize a highly-reliablesolid-state imaging device having excellent color characteristics.

FURTHER INFORMATION ABOUT TECHNICAL BACKGROUND TO THIS APPLICATION

The disclosure of Japanese Patent Application No. 2004-296672 filed onOct. 8, 2004 including specification, drawings and claims isincorporated herein by reference in its entirety.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, advantages and features of the invention willbecome apparent from the following description thereof taken inconjunction with the accompanying drawings that illustrate a specificembodiment of the invention. In the Drawings:

FIG. 1 is a sectional view of a conventional solid-state imaging devicehaving color filter layers which are made of pigment dispersion typecolor resists;

FIG. 2 is a sectional view of a conventional solid-state imaging devicehaving color filter layers which are made of dye-containing type colorresists;

FIG. 3 is a sectional view of another conventional solid-state imagingdevice having color filter layers which are made of dye-containing typecolor resists;

FIG. 4 is a diagram showing the sectional structure of a solid-stateimaging device concerning the embodiment of the present invention;

FIG. 5 is a sectional view of the solid-state imaging device of thepresent invention in its manufacturing process until a surfaceprotection film 18 is formed on the N-type semiconductor substrate 11;and

FIG. 6 is a sectional view of the solid-state imaging device of thepresent invention in its manufacturing process until a first colorfilter layer 21G for green is formed on the N-type semiconductorsubstrate 11.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

FIG. 4 is a diagram showing the sectional structure of a solid-stateimaging device concerning the embodiment of the present invention. Notethat sectional views of two photoelectric conversion elements 13 areshown in the figure.

As shown in FIG. 4, this solid-state imaging device 1 includes: a firstconductive type (for example, N-type) semiconductor substrate (N-typesemiconductor substrate) 11; a second conductive type (for example,P-type) first semiconductor well (P-well layer) 12; photoelectricconversion elements 13; a gate insulation film 14; a conversionelectrode 15; an inter-layer insulation film 16; a light-shielding film17; a surface protection film 18; a first transparent planarization film19; a resin part 20; a color filter layer 21; a second transparentplanarization film 22 and a microlens 23.

On the surface of the N-type semiconductor substrate 11, the P-welllayer 12 having inverse characteristics of the N-type semiconductorsubstrate 11 is formed. On the surface of the P-well layer 12 N-typesemiconductor regions are formed, which forms a matrix of photoelectricconversion elements 13. On the surfaces of the P-well layer 12 and eachphotoelectric conversion element 13 the gate insulation film 14 isformed.

Further, on the gate insulation film 14 in the boundary region betweenphotoelectric conversion elements 13, the conversion electrode 15 madeof polycrystalline silicon is formed. On the surface of the conversionelectrode 15 the inter-layer insulation film 16 is formed so that theinter-layer insulation film 16 covers the conversion electrode 15. Onthe inter-layer insulation film 16 the light-shielding film 17 made of,for example, tungsten is formed, the inter-layer insulation film 16being formed on the gate insulation film 14 excluding the part above theapertures of photoelectric conversion elements 13. Further, on thesurface of the light-shielding film 17 and the gate insulation film 14,the surface protection film 18 made of a SiON film and the like isformed. As the result, conversion electrodes 15 and the like are formedas convex parts on the respective photoelectric conversion elements 13.

In order to form the color filter layer 21 accurately later on,well-known processes of coat, exposure and development processes areperformed using a transparent photosensitive film which is mainly madeof a phenol resin and the like. Consequently, each concave part isfilled with the surface protection film 19 so that the surface of thesurface protection film 19 becomes flush with the highest surfaces ofthe surface protection films 18.

First, one of the following is coated: a negative type photosensitiveacrylic resin (transparent resin) which is obtained by removing apigment component or a dye component from the materials of the colorfilter layers 21; and a colored negative type photosensitive acrylicresin which is obtained by adding a black pigment or a black dye to thistransparent resin. Next, exposure and development processes areperformed using a mask which is designed to be narrower than thelight-shielding film 17. In this way, each resin part 20 is formed onthe surface protection film 18 which covers the light-shielding part 17so that it becomes an upward convex part having a dimension narrowerthan the surface protection film 18.

After that, a first color filter layer 21G is formed by coating a firstcolor filter layer material (for example, green), and performingexposure and development processes using a mask which is designed toform a color filer layer 21 at a desired position. Note that in the caseof using a dye-containing type color resist as a material for a colorfilter layer 21, performing the PEB process after exposure makes itpossible to improve the stability and the sectional shape of the colorfilter layer 21. After that, a second color filter layer 21B (forexample, blue) and a third color filter layer 21R (for example, red) areformed in sequence. In other words, each of the color filters 21G, 21Band 21R is formed in a way that it covers the area ranging from thesummit of a resin part 20 to the next summit of an adjacent resin part20, and each of the color filters 21G, 21B and 21R is thicker in the topsurface than the peripheral part. Consequently, those color filterlayers 21G, 21B and 21R function as concave lenses respectively.

Further, in order to form each on-chip microlens 23 accurately later on,a second transparent planarization film 22 is formed by coating atransparent resin which is mainly made of acrylic resin several times,baking and then dry-etching the coated transparent resin using anetch-back method.

After forming the second transparent planarization film 22, theprocesses of coating, exposure and development of the transparent resinare performed to form each on-chip microlens 23.

In this way, with the resin part 20, later-formed color filter layers21G, 21B and 21R are slimmed down in the boundaries between each otheras compared to the part above the photoelectric conversion elements 13,making each of them function as a concave lens, and thus it becomespossible to improve the light condensing efficiency and the sensitivityof each filter. Further, it becomes possible to form color filters 21G,21B and 21R accurately, which makes it possible to prevent color mixturebetween adjacent elements which occurs depending on a dimensionalaccuracy and to improve the problems of nonuniform tone of lines,sensitivity variations and color shading.

Note that the resin part 20 is made of a material having a refractiveindex lower than that of the color filter layer 21, the color filterlayer 21 is made of a material having a refractive index higher thanthat of the transparent planarization film 19, the second transparentplanarization film 22 is made of a material having a refractive indexlower than that of the color filter layer 21, and the microlens 23 ismade of a material having a refractive index higher than that of thecolor filter layer 21.

Therefore, this structure provides an effect of reducing incident lightfrom an adjacent pixel when oblique incident light reaches theperipheral part. In addition to this, the lens effects provided by thecolor filter layer 21 and the microlens 23 enables to condense lightgradually and efficiently, the color filter layer 21 serving as aconcave lens and the microlens 23 serving as a convex lens. Thus it isexpected that its sensitivity is improved.

Next, the manufacturing method of a solid-state imaging device 1 formedin this way will be described with reference to FIGS. 4, 5 and 6.

FIG. 4 is a sectional view of the solid-state imaging device of thepresent invention. FIGS. 5 and 6 each is a diagram showing the sectionalview of the solid-state imaging device, the section view illustratingthe order of the manufacturing processes of the solid-state imagingdevice.

FIG. 5 is a sectional view of the solid-state imaging device of thepresent invention in its manufacturing process until a surfaceprotection film 18 is formed on the N-type semiconductor substrate 11

The manufacturing method illustrated by the figure will be describedbelow with reference to the following (1) to (4).

(1) First, P-well layers 12 having inverse characteristics of the N-typesemiconductor substrate 11 are formed like a matrix on the surface ofthe N-type semiconductor substrate 11 so as to form an N-type dispersionlayer (photoelectric conversion element) 13 on each of these P-welllayers 12. In general, the P-well layer 12 and the N-type dispersionlayer (photoelectric conversion element) 13 are formed by repeating thephotolithographic process, the ion implantation process, and the thermaldispersion process.

(2) After the photoelectric conversion elements 13 are formed, a gateinsulation film 14 is formed on the surfaces of the P-well layers 12 andthe photoelectric conversion elements 13. After that, in order to fillthe apertures of the photoelectric conversion elements 13, thefollowings are respectively formed on the gate insulation film 14 in theboundaries between the photoelectric conversion elements 13: aconversion electrodes 15 which is made of conductive polycrystallinesilicon; inter-layer insulation films 16 which electrically insulatethese conversion electrodes 15 by covering them; and light-shieldingfilms 17 which is made of tungsten.

(3) After the light-shielding films 17 are formed, a surface protectionfilm 18 is formed on the surfaces of the gate insulation film 14 and thelight-shielding films 17, the surface protection film 18 being, forexample, a BPSG film (boron-phospho-silicate glass) or a SiON filmobtained through a thermal flow process. At this time, a concave part isformed above each photoelectric conversion element 13 because ofconversion electrodes 15 and the like.

(4) Further, after the wire (not shown) made of aluminium and the likeis formed, for example, a SiON film and a bonding pad (not shown) forextracting electrodes are formed.

FIG. 6 is a sectional view of the device in its manufacturing processduring which up to first color filter layers G for green are formed. Themanufacturing process performed until the sectional shape in the figureis obtained will be described in the following (5) to (8).

(5) First, as a preparation for forming the color filter layers 21accurately later on, transparent planarization resin films 19 are formedin the concave parts above the photoelectric conversion elements 13 byperforming the following processes: coating of a transparentphotosensitive resin which is mainly made of, for example, a phenolresin, on the surface protection film 18; and performs the processes ofexposure and development of the resulting resin surface.

(6) Next, one of the following is performed: coating of a thin filmwhich is made of, for example, a transparent thermal curing type acrylicresin and performs thermal curing of the resulting resin layer; andvapor-coating of an HMDS film. After that, as a preparation for formingthe color filter layers 21 accurately later on, for example, a negativetype photosensitive resin is coated and the resulting resin layer isexposed and developed so as to form, in a frame form, resin parts 20 onthe non-light-receiving area. Each of the resin parts 20 has an upwardconvex sectional shape and the width is equal to or smaller than thewidth of the light-shielding film 17. The non-light-receiving area ismade of conversion electrode 15, a light-shielding film 17 and the like.In other words, each non-light-receiving area is between photoelectricconversion elements 13 which are adjacent to each other, and theposition becomes a boundary of color filter layers 21 to be formed lateron.

Note that the mask used at this time is a mask designed to be narrowerthan a light-shielding film 17, however, it is also possible to use amask designed for a microlens 23 at the same time. Also, an examplematerial used for this resin part 20 is as follows: a negative typephotosensitive acrylic resin (transparent resin) obtained by removing apigment component or a dye component of a color resist to be used lateron; or a colored negative type photosensitive acrylic resin obtained byadding a black pigment or a black dye to the negative typephotosensitive acrylic resin. Note that a transparent resin is used inthis embodiment. Also, it is more effective that the refractive index ofthe resin part 20 is lowered than that of each color filter layer 21 tobe formed later on.

(7) After the resin parts 20 are formed, one of the followings isfurther performed: coating of a thin film made of a transparent thermalcuring type acrylic resin or the like and performing a thermal curingprocess of the resulting thin film; and vapor-coating of an HMDS filmand then, for example, a resist for forming a color filter layer 21G forgreen in sequence. This resist is prepared to contain a pigment or a dyewhich allows only green wavelength light to pass itself through.

(8) Sequentially, the resin-coated color resist is exposed and developedusing a photomask designed for forming a green color filter layer 21G oneach desired photoelectric conversion element 13. By performing theabove-described processes, a green color filter layer 21G whosesectional shape becomes a concave lens is formed. Note that, in the casewhere a dye-containing type color resist is used as a color filter layermaterial, performing the PEB process after exposure makes it possible toimprove the stability as a color filter material and the sectionalshape.

FIG. 4 shows a sectional view of the device in its manufacturingprocesses starting with the formation of the green color filter layer 21and ends with the formation of the microlens 23. The manufacturingprocesses performed until the sectional shape shown in the figure isobtained will be described in the following (9) to (12).

(9) After a green color filter layer 21G is formed, a blue color filterlayer 21B and a red color filter layer 21R are formed, a blue colorfilter layer 21B and a red color filter layer 21R are respectivelyformed at determined positions in the same way used for a green colorfilter layer 21G.

(10) Further, in order to form on-chip microlens 23 to be formedaccurately later on, a second transparent planarization film 22, whichis for planarizing the surface realized after the color filter layer 21is formed, is formed by repeating the following processes: coating atransparent thermal curing resin which is mainly made of, for example,an acrylic resin on each of the color filter layers 21G, 21B and 21Rseveral times, and then performing a bake process for causing thermalcuring of the resin.

(11) After that, in order to shorten the distance from a light receivingsurface to each of the color filter layers 21G, 21B and 21R with apurpose of improving the sensitivity of each filter, etching of thesecond transparent planarization film 22 is performed as deep aspossible according to a well-known etch back method.

(12) After that, an on-chip micro lens 23 having an upward convex shapeis formed through the following processes: coating of a transparentpositive type photosensitive resin which is mainly made of a phenolresin on the surface of the second transparent planarization film 22above each photoelectric conversion element 13; exposure of the resin;and development (including breeching and baking) of the exposed resin.The spectral transmittance of each on-chip microlens 23 is improved bythe irradiation of ultra violet rays. Note that the post-baketemperature of the microlens 23 needs to be adjusted to 200 degrees orbelow in order to prevent the deterioration of the spectralcharacteristics of the color filter layers 21G, 21B and 21R. Also, it isrequired that: the refractive index of the first transparentplanarization film 19 is lower than that of the color filter layer 21;the refractive index of the second transparent planarization film 22 islower than those of the color filter layers 21G, 21B and 21R; and therefractive index of each on-chip microlens 23 is higher than that of thesecond transparent planarization film 22.

The solid-state imaging device 1 shown in FIG. 4 can be manufactured byperforming the above-described processes.

With each resin part 20, it becomes possible to expect that the effectof a concave lens is obtained because color filter layers 21G, 21B and21R to be formed later on can be slimed down in each boundary than inthe part above each photoelectric conversion element 13. Therefore, thelight condensing rate of each filter is increased, and thus itssensitivity is improved.

Further, it becomes possible to form color filter layers 21G, 21B and21R accurately. Also, when oblique incident light reaches the surface,it is possible to prevent color mixture between adjacent elements, thecolor mixture occurring depending on dimensional accuracy. This makes itpossible to improve the problem of nonuniform tone of lines, sensitivityvariations and color shading.

As described up to this point, the solid-state imaging device in thisembodiment of the present invention makes it possible to form colorfilter layers 21 having an improved sectional shape and an excellentdimensional accuracy by means of: forming of resin parts at eachboundary between adjacent color filter layers 21 which will be formedlater on, the resin parts having an upward convex section which isvertical to the boundaries; and then forming of the respective colorfilter layers 21 in order to cover the resin parts.

Consequently, it becomes possible to prevent color mixture from adjacentcolor filter layers 21 because of oblique light, and thus thesolid-state imaging device can realize high-definition images.

Further, making the refractive indexes of the resin parts 20 formed ateach boundary lower than those of the color filter layers 21 providesthe effect of reducing the incident light coming from adjacent pixels.

Also, these color filter layers 21 have a concave lens shape and therefractive index which is higher than that of the second planarizationfilm. This makes it possible to condense incident light on eachphotoelectric conversion element 13 efficiently, and thus it becomespossible to improve its sensitivity.

Further, since color filter layers 21 can be slimmed down in theperipheral parts, it becomes possible to accurately form the respectivecolor filter layers 21 on photoelectric conversion elements 13. Thisresults in eliminating color-shading between pixels, and consequently,the solid-state imaging device can improve the problems of nonuniformtone of lines and color shading.

Also, since spectral dispersion of these color filter layers 21 is lowerin their peripheral parts than in their center parts, light transmissionfrom the peripheral parts of these color filter layers 21 increasescompared to the case of a conventional structure. Consequently, thesolid-state imaging device can have an improved sensitivity.

Further, the refractive indexes of on-chip microlenses 23 formed on thesecond transparent planarization films 22 are higher than those of thesecond planarization films, it becomes possible to efficiently condenseincident light that reaches the microlenses 23 on the photoelectricconversion elements 13. Consequently, the sensitivity of the device isimproved.

Note that methods for forming transparent planarization resin films 19below these color filter layers 21 include: (a) a method for coating atransparent photosensitive film, and performing exposure and developmentprocesses so as to fill the concave parts in the ground layer; (b) amethod for coating a transparent film several times and performingplanarization according to a well-known etch back method; (c) a methodfor coating a transparent film and performing planarization through athermal flow process; and (d) a combination method of the above-listedmethods for improving planarization level.

A resin part 20 can be obtained in the following way: coating of a blackpigment dispersion type color resist or a black dye-containing typecolor resist; and then performing of exposure and development processesusing a mask for forming a microlens 23 or a photomask designed to besmaller than the light-shielding area.

This manufacturing method enables to manufacture the solid-state imagingdevice having the structure, action and effect that are described above.

The solid-state imaging device and the manufacturing method of thesolid-state imaging device in the embodiment of the present inventionhave been described up to this point. However, this invention is notlimited to the embodiment, in other words, variations can be appliedwithout deviating from the scope of the present invention.

For example, there has been described a method of employing primalcolors for color filter layers 21, the primary colors are used forrealizing a tone-oriented solid-state imaging device. However, a methodof employing complementary colors may be applied in the case where adesired solid-state imaging device is a resolution and sensitivityoriented one. In the latter case, color filters for mazenta, yellow andcyan are formed at predetermined positions according to a well-knowncolor alignment so as to form color filter layers.

Also, materials for forming such color resist layers include a colorresist containing a dye, a color resist containing a pigment and thelike, and any one of them can be selected.

Also, there has been described a well-known photolithographic techniqueaccording to which a first transparent planarization film 19 is made ofa transparent photosensitive resin. However, there is a formationmethod, according to a well-known etch back method, of repeating theprocesses of: coating a transparent thermal curing resin materialseveral times; and then performing thermal curing of the resin.

After the first transparent planarization film 19 is formed, atransparent thermal curing type resin which is mainly made of acrylicresin or an HMDS film is used for improving adhesion between a resinpart 20 and a color filter layer 21. However, they can be omitted aslong as the adhesion strength is guaranteed.

Also, the solid-state imaging device described in the embodiment is CCDtype. However, the type is not limited to CCD type, in other words, anamplifier type solid-state imaging device such as MOS type or anothertype solid-state imaging device can also be applied.

Although only an exemplary embodiment of this invention has beendescribed in detail above, those skilled in the art will readilyappreciate that many modifications are possible in the exemplaryembodiment without materially departing from the novel teachings andadvantages of this invention. Accordingly, all such modifications areintended to be included within the scope of this invention.

Industrial Applicability

The present invention is suitable for a solid-state imaging deviceincluding: photoelectric conversion elements 13 which are formed on asemiconductor substrate 11; conversion electrodes 16 which are formedaround these photoelectric conversion elements 13; color filter layers21 which are formed on these photoelectric conversion elements 13; andmicrolenses 23 formed on these color filter layers 21.

What is claimed is:
 1. A solid-state imaging device comprising: asemiconductor substrate on which a plurality of photoelectric conversionelements are formed; a first transparent planarization film formed abovesaid semiconductor substrate and above said photoelectric conversionelements; a surface protection film formed above said semiconductorsubstrate and above a boundary area between said photoelectricconversion elements adjacent to each other; a convex part formed on saidsurface protection film and above the boundary area; and a color filterformed above said first transparent planarization film and said convexpart and above said photoelectric conversion elements, wherein saidcolor filter has a concave top surface.
 2. The solid-state imagingdevice according to claim 1, wherein said surface protection film is aSiON film.
 3. The solid-state imaging device according to claim 1,wherein said first transparent planarization film is mainly made ofphenolic resin.
 4. The solid-state imaging device according to claim 1,wherein said color filter is thinner in a peripheral part than in acenter part.
 5. The solid-state imaging device according to claim 1,wherein said convex part has a lower refractive index than said colorfilter.
 6. The solid-state imaging device according to claim 1, whereinsaid color filter has a higher refractive index than said firsttransparent planarization film.
 7. The solid-state imaging deviceaccording to claim 1, further comprising a second transparentplanarization film formed on said color filter, wherein said secondtransparent planarization film has a lower refractive index than saidcolor filter.
 8. The solid-state imaging device according to claim 7,further comprising a microlens formed on said second transparentplanarization film, wherein said microlens has a higher refractive indexthan said second transparent planarization film.
 9. The solid-stateimaging device according to claim 7, further comprising a microlensformed on said second transparent planarization film, wherein saidmicrolens has a higher refractive index than said color filter.
 10. Thesolid-state imaging device according to claim 1, wherein said convexpart is formed in a matrix shape above the boundary area.
 11. Thesolid-state imaging device according to claim 1, wherein said convexpart is mainly made of resin.
 12. The solid-state imaging deviceaccording to claim 1, wherein said color filter has an edge part locatedon a summit of said convex part.